A device which utilizes two small disc targets to check the boresighting adjustments of the telescopes mounted on a weapon, without the aid of a test target or distant aiming point.It consists of an expansion mandril which is inserted into a gun tube, and a hinged arm to which the targets are secured. The arm protrudes from the muzzle of the weapon at a right angle to the weapon tube, and may be used on weapons equipped with, or without a muzzle brake.